Since September 11 in U.S., security-inspection of aviation is becoming more and more emphasized. Besides conventional security-inspection of packages, security-inspection of the liquid articles carried by passengers is added. Accordingly, it is in dire need of means and methods for quick security-inspection of the liquid articles.
Nowadays, there are four types of methods used in security-inspection of liquid articles, including chemical method, electromagnetic method, neutron detection method and radiation detection method as follows:
1) The chemical method can be subdivided into odor identification method, ion scanning explosive detection method and substance analysis method. The odor identification in practical applications often fails to implement detection because of sealed and packaged conditions of liquid articles. The ion scanning explosive detection method is known for its high sensitivity, but with high false alarm rate, it suffers from the affection of background environment. The substance analysis is of high precision and high accuracy, but this method needs a certain period of time to analyze the sample, which cannot meet the demands of on-site quick detection.
2) The electromagnetic method works in an active measurement manner. It distinguishes liquid articles from each other according to their dielectric constants in an electromagnetic field. The electromagnetic method is easily subjected to severe affection of metal packages or other thick material packages. As a result, the use of electromagnetic method is limited in case of complex package materials.
3) The use of the neutron detection method will leave residual radiation remaining in the detected liquid due to the effect of “neutron activation”. Furthermore, the radiation shielding is complicate due to neutrons' strong penetrability, and the apparatus has to take a large area, so the method is not suitable for application in the security-inspection systems of civil aviation.
4) Currently, most of the security-inspection apparatuses for civil aviation are radiation apparatuses. In these apparatuses, the 2D X-ray imaging technology and three-dimensional CT technology are mostly adopted. These technologies, which can obtain structure information of articles, fail to determine whether there are drugs concealed in the liquid articles. The reason is that the overall structure (for example, the number of layers) of the liquid articles will not change a lot with drugs being concealed therein, only the components will change.
To sum up, for the quick detection of the liquid articles, the chemical method, the electromagnetic method and the neutron detection method are not suitable. By using the 2D X-ray imaging technology and the three-dimensional CT technology, images including the structure information of the article are acquired, but these images cannot work as sufficient evidence for whether there are drugs concealed in the liquid articles.